1. Field of the Invention
The present invention relates to a semiconductor device having an island portion for mounting a semiconductor chip thereon.
2. Description of the Related Art
A relatively high demand for performance of an electronic component relates to downsizing and thinning of the package. It is thus considered that while pursuing the downsizing and thinning during development, technological evolution, such as represented by material developments, structural investigations, and developments and reconsiderations of process, has been simultaneously advanced. The necessity of pursuing the downsizing and thinning of the electronic component as described above resides in that the electronic component is required to be downsized and thinned in proportion to the downsizing and thinning of the device on which the electronic component is to be mounted, which shows that the products have become diversified. In particular, for a semiconductor component, generally a resin-molded package form is often used.
A configuration of the resin-molded package can be roughly classified into a configuration using a resin substrate and an epoxy resin mold and a configuration using a lead frame and an epoxy resin mold. What is common to the downsizing and thinning of the resin-molded package using the resin substrate and the resin-molded package using the lead frame is to pursue the design with the small, fine, and thin dimensions of the respective components. As a result, such adverse effects appear that the reliability is insufficient and the package is weak. Therefore, it is necessary to make a review in order to improve the reliability of the electronic component to be further downsized and thinned. The resin-molded package as represented by the semiconductor component is subject to significant change in size. As the product size of the resin-molded package becomes smaller and thinner, maintaining the reliability is difficult and thus is important, which requires new approaches.
FIGS. 7A and 7B illustrate an island including a mounting region on which a semiconductor chip is to be mounted in a semiconductor package, FIG. 7A being a plan view of the island and FIG. 7B being a sectional view of the island (see, for example, Japanese Published Patent Application No. 2006-156437). The island has a considerably larger size than that of the semiconductor chip and includes a plurality of grooves formed in its surface. Referring to the description, each of the grooves has a width of about 0.2 mm and a depth of about 0.1 mm to 0.2 mm, and the grooves are arranged in a grid pattern. Further, the grooves arranged in a grid pattern are formed in a region having a larger size than that of the semiconductor chip. When the semiconductor chip is firmly mounted on the island through intermediation of a silver paste, the silver paste applied at this time enters the groove portions and the excessive silver paste that is further spread to the side peripheral portion of the semiconductor chip is guided into the grooves. Hence, it is possible to reduce the amount of the silver paste creeping up along the side surface of the chip, and prevent the silver paste from creeping up on the semiconductor chip surface.
However, because the island structure described in Japanese Published Patent Application No. 2006-156437 has the grooves in a grid pattern formed in the region having a larger size than that of the semiconductor chip, the island and the region for forming the grooves in a grid pattern always need to have considerably larger sizes than the semiconductor chip size. Hence, a large island size is necessary. This structure is thus not appropriate for the package to which downsizing is required since in downsizing the package in this case it is difficult to design the sizes of the island and the region in the island, which is used for forming the grooves in a grid pattern and which has a larger size than the semiconductor chip, to be close to the semiconductor chip size.
Further, the island structure described in Japanese Published Patent Application No. 2006-156437 has the plurality of grooves formed in a grid pattern each having a width of about 0.2 mm and a depth of about 0.1 mm to 0.2 mm. In a case where the semiconductor chip size is also downsized in the package that is required to be downsized and thinned, when the necessary width of the grooves is 0.2 mm, the semiconductor chip may be mounted in a tilted manner. Further, the thinned package often uses a sheet material having a thickness of 0.2 mm to 0.1 mm or less for the island portion and the lead frame portion. It is thus difficult to form the grooves in a grid pattern each having a necessary depth of about 0.1 mm to 0.2 mm. When the plurality of grooves in a grid pattern each having the width and depth of about 0.2 mm are formed in the island, the difficult processing leads to the increase in the processing cost and processing time. Therefore, the structure described in Japanese Published Patent Application No. 2006-156437 in which the grooves are processed in the island portion is difficult to be applied to the package design that is required to be downsized and thinned and thus increases the cost.
Further, some semiconductor packages include a plurality of semiconductor chips mounted thereon. In a case where the plurality of semiconductor chips are mounted on the island or in a case of a multichip semiconductor product including a further number of semiconductor chips mounted thereon, processing the same number of grooves as that of the semiconductor chips to be mounted on the island portion not only complicates the processing but also further increases the island size and cost. Hence, the application of such a structure tends to be difficult.
Further, an insulating paste is sometimes used as an adhesive for fixing the island portion and the semiconductor chip. Using a silver paste may cause migration of silver due to creeping up in the silver paste and bleed-out in which silver in the silver paste and a resin are separated from each other, which contribute to reduction of the reliability. Thus, more products have used the insulating paste not containing a silver filler. Because no silver filler is contained, the insulating paste has a higher resin ratio as compared to that of the silver paste and thus has a relatively low viscosity in many cases. For this reason, controlling the insulating paste has difficulties as compared to handling the silver paste. Specifically, due to the reduced surface tension, the paste is wet-spread after the application and it is difficult to secure the thickness and set the paste shape to have a hemispherical shape after the application. When the island having the grooves in a grid pattern is applied with the insulating paste, the paste mostly enters the grooves and then is spread around, and hence the insulating paste hardly remains on the fixing contact surface between the island surface and the semiconductor chip. Further, the insulating paste entering the inside of the grooves tends to be pulled by the contacts between the paste and the both side surfaces of the grooves and have a shape with the recessed surface, and hence a clearance is liable to be formed between the semiconductor chip and the island. This leads to an insufficient adhesive strength.
In addition, in a case where the island portion and the semiconductor chip are fixed to each other, because the adhesive thickness obtained when the semiconductor chip is mounted is, in a case of the silver paste, substantially proportional to the silver filler size, the silver paste thickness of at least about 20 μm is formed between the island portion surface and the semiconductor chip. Hence, a sufficient thickness and an adhesive strength can be obtained. When the insulating paste is used, filler is not contained, or silica filler or the like is used in many cases. The thickness obtained owing to the silver filler cannot be secured in this case, and the thickness is equal to or less than 5 μm in many cases even if the filler is contained. Accordingly the paste thickness formed between the island portion surface and the semiconductor chip is as thin as about a few μm, and this tends to reduce the adhesive strength.
Under such circumstances, attempts have been made for devising a processing method and a structure of the island portion that are aimed at improving the adhesive force between the island portion and the semiconductor chip by using the insulating paste or the silver paste. With regard to the structure having the grooves formed therein, the grooves are formed linearly, roundly or in a grid pattern, to thereby improve the adhesive strength of the insulating paste with a lowered viscosity so that it easily flows. Further, another attempt has been made for improving the adhesive strength between the semiconductor chip and the insulating paste by subjecting the island portion surface to roughening processing and forming fine irregularities on the island portion, to thereby improve the adhesive strength between the semiconductor chip and the island surface that are fixed to each other.